1. Field of the Invention
The present invention relates to a scroll-type fluid displacement apparatus, and more particularly, to a scroll-type fluid compressor having improved scroll members.
2. Description of Related Art
Scroll-type fluid displacement apparatus, which having a fixed scroll member and an orbiting scroll member, are known in the art. Referring to FIG. 5, a known scroll-type fluid displacement apparatus is shown in the form of scroll-type compressor unit 50. Compressor unit 50 includes cup-shaped casing 1, front housing 2, orbiting scroll member 10 and fixed scroll member 11. Front housing 2 is funnel-shaped and is fixed to the open side of cup shaped casing 1 by a plurality of screws (not shown).
Annular sleeve 2a projects from the center portion of front housing 2. Drive shaft 3 penetrates annular sleeve 2a and reaches the inside of cup-shaped casing 1. Drive shaft 3 is rotatably supported by annular sleeve 2a through bearings 4 and 5. Drive apparatus 6 is secured on the projecting part of drive shaft 3, which projects from front housing 2. Drive apparatus 6 comprises pulley 7 and electromagnetic clutch 8. An external driving force (not shown) rotates pulley 7, and a transmission device (not shown) transmits the driving force of the external driving force. Pulley 7 is rotatably supported by the projecting part of housing 2. Electromagnetic clutch 8 transmits a rotating force of pulley 7 to drive shaft 3, or disconnects a rotating force of pulley 7 from drive shaft 3.
Orbiting scroll member 10 and fixed scroll member 11 are disposed in cup-shaped casing 1. Fixed scroll member 11 is disposed in the bottom portion of cup-shaped casing 1, and orbiting scroll member 10, which interfits with fixed scroll member 11, is disposed in the open side of cup-shaped casing 1. Fixed scroll member 11 is secured on cup-shaped casing 1 by a plurality of screws 25, which thread from the outside of the bottom portion of cup-shaped casing 1.
Orbiting scroll member 10 comprises first end plate 13 and first spiral element 14, which is formed on first end plate 13. Orbiting scroll member 10 is eccentrically connected to drive shaft 3. Therefore, orbiting scroll member 10 is driven in an orbital motion by the rotation of drive shaft 3 in cup-shaped casing 1.
Fixed scroll member 11 comprises second end plate 16 and second spiral element 17, which is formed on second end plate 16. Discharge chamber 12 is defined by the bottom of the inner surface of cup-shaped casing 1 and second end plate 16. Discharge port 15 is formed in the central part of second end plate 16. Reed valve 20, which is plate-shaped, is formed to be movable on discharge port 15 between a closed position and an open position. Valve retainer 21 is formed on reed valve 20 to limit the open movement to a predetermined amount or degree.
Second end plate 16 isolates two chambers in cup-shaped casing 1, discharge chamber 12 and suction chamber 23. Orbiting scroll member 10 is disposed in suction chamber 23, which sucks refrigerant gas from the outside. First spiral element 14 of orbiting scroll 10 and second spiral element 17 of fixed scroll member 11 interfit at a predetermined angular offset.
The side wall part of cup-shaped casing 1 has inlet port 31, which sucks refrigerant gas, and outlet port 32, which discharges compressed fluid. Outlet port 32 communicates discharge chamber 12 with the outside of the compressor.
In this structure of a scroll-type fluid displacement apparatus, when a driving force is transmitted from an external drive source, e.g., an engine of a vehicle, via drive apparatus 6, drive shaft 3 is rotated, and orbiting scroll member 10 is driven in an orbital motion by the rotation of drive shaft 3. When orbiting scroll member 10 moves in an orbital motion, the fluid pockets, which are formed between fixed scroll member 11 and orbiting scroll member 10, move to the center with a consequent reduction in volume. Finally, the fluid pockets move to and are forced through discharge port 15, and open reed valve 20. The compressed fluid in the discharge chamber 12 is discharged into a refrigerant circuit (not shown) through outlet port 32 disposed on cup-shaped casing 1.
Bearing member space 19 is formed around bearing 4, which is disposed between drive shaft 3 and front housing 2. Bearing member space 19 communicates with fluid suction space side of orbiting scroll 10 through a hole formed in housing 2 (not shown). Balance weight 26 is fixed to orbiting scroll 10 through eccentric bush 27.
FIGS. 6a to 6c depict a plan, cross-sectional view of orbiting scroll member 10 of FIG. 5. Conventionally, first end plate 13 of orbiting scroll member 10 is formed with a uniform plate thickness throughout. As shown in FIG. 6b, in order to prevent cracks in the central end part of first spiral member 14, however, the plate thickness of the central part of first end plate 13 tends to be thicker than the rest of end plate 13. This is because the majority of the stress is concentrated at the collecting portion of the spiral wall of first spiral member 14 and first end plate 13. For example, a known scroll member is disclosed in Japanese Patent Application JP-A-5-106568.
FIGS. 7a to 7c depict a plan, cross-sectional view of fixed scroll 11 member of FIG. 5. Conventionally, second end plate 16 of fixed scroll 11 has a uniform thickness throughout.
In a known scroll-type fluid displacement apparatus, the plate thickness of the central part of first end plate 13 is thicker than the rest of end plate 13 in order to prevent cracks in the central end part of first spiral member 14. Therefore, there are problems with the increased weight of orbiting scroll member 10, which causes the weight of a scroll-type fluid apparatus to increase. It is difficult to reduce the weight of fixed scroll member 11, because second end plate 16 of fixed scroll 11 is formed with a uniform thickness. Therefore, it is difficult to reduce the weight of a scroll-type fluid apparatus.